Field of the Invention
This invention relates to a multi-level ground water characterization method and apparatus using flexible borehole liners and associated components to perform water level and ground water sampling in subsurface boreholes.
Background Art
A “borehole” is a hole, e.g., a drilled shaft, into the Earth's subsurface. Borehole hydraulic conductivity profiling techniques described in my U.S. Pat. Nos. 6,910,374 and 7,281,422 have been used in many boreholes over the past decade or so. These patents, whose teachings are hereby incorporated by reference, describe the hydraulic transmissivity profiling technique which carefully measures the eversion of a flexible borehole liner into an open stable borehole. Other installations of flexible liners into boreholes, by the eversion of the liners, are used in a variety of systems and methods disclosed in several of my other patents. Those liners are usually installed into the open boreholes using a water level inside the liner that is significantly higher than the water table in the geologic formation penetrated by the borehole. The use of the continuous flexible liner has a sealing advantage and other advantages as manifest in my other systems and techniques.
Over time, several methods for measuring subsurface hydrologic characteristics have been developed. The several methods have a different means of isolating discrete sampling elevations in a single borehole, obtaining ground water samples for analysis and measuring the water table at each sampling elevation. Most known methods of isolating each sampling elevation from those adjacent sampling elevations range involve various types of packers (an inflated bladder) or cast sealants, such as bentonite or grout. It also is known to isolate sampling levels using a flexible liner. The use of a flexible liner is not unique to the present disclosure.
The eversion of a flexible liner into position in the borehole does require procedures that can be slow and labor intensive in the situation of a small diameter borehole and with relatively low borehole transmissivity. Pumping the water from beneath the liner and erecting a scaffolding to achieve a sufficient driving pressure (in shallow ambient water tables) are two features that are avoided by the present system and method, in one application. It is also a limiting factor of the current flexible liner based multi-level systems that the bulk and weight of the systems prevent some attractive installation methods possible with this presently disclosed innovation.